Concurrent reduction for improving the performance of the dehydrogenation of alkanes

ABSTRACT

A process of catalytically dehydrogenating an alkane to an alkene, using Cr2O3 as a catalyst, where the catalyst is reduced concurrently with the dehydrogenation by using CO as a reducing gas. In reducing the catalyst with CO, CO2 is produced, which may be reacted with H2 produced by the dehydrogenation, to form CO and H2O by the reverse water-gas shift reaction. A Cu O heat-releasing material may be included with the catalyst in the reactor. The CO reducing gas reduces CuO to form Cu and CO2, releasing heat. The CO2 produced by reducing the Cu O may also be reacted with H2 produced by the dehydrogenation, to form CO and H2O by the reverse water-gas shift reaction.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 371 of International Application No.PCT/IB2015/059118, filed Nov 25, 2015, which claims priority to U.S.application Ser. No. 62/085,234, filed Nov. 26, 2014 which areincorporated herein by reference in their entirety.

BACKGROUND FIELD OF THE INVENTION

The present invention relates to processes for dehydrogenating alkanesto alkenes, specifically alkane dehydrogenation processes using achromium oxide catalyst, a method for decreasing the temperature and/orincreasing the efficiency of an alkane dehydrogenation process, and acomposition formed by dehydrogenating an alkane with a chromium oxidecatalyst.

DESCRIPTION OF THE RELATED ART

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentinvention.

Alkenes are one of the most important feedstocks for industrial chemicalpurposes, since they can participate in a wide variety of reactions. Forexample, ethylene and propylene can be polymerized to form polyethyleneand polypropylene, respectively, and isobutylene can be reacted withmethanol to form methyl tert-butyl ether (MTBE). Alkenes, however, arefar less naturally abundant than their alkane counterparts.

Alkanes are obtained in abundant quantities as byproducts of fossil fuelrefining processes, and are useful precursors for the more industriallyrelevant alkenes. For example, alkenes are produced from alkanesindustrially by thermal cracking and steam cracking Alkanes also may becatalytically dehydrogenated to alkenes by the following endothermicreaction:C_(n)H_(2n+2)→C_(n)H_(2n)+H₂ΔH_(R)°>0   (R1)Hydrogen-containing gases, such as H₂ and CH₄, are typically used in areduction cycle, for example reducing the chromium from an oxidationstate of Cr⁶⁺ to Cr³⁺ in a chromium oxide catalyst.

Because alkane dehydrogenation reactions are highly endothermic, theyrequire high temperatures to obtain acceptable yields. However, thesehigh temperatures enhance undesired side reactions, including theformation of carbonaceous coke deposits on the catalyst bed. Cokebuildup adversely affects catalyst₊performance, leading to lower yieldsand expensive maintenance. For example, once catalysts have beendeactivated by coke buildup, the dehydrogenation process must be takenoffline and so that the catalyst may be regenerated, typically byburning off the coke deposits with air. This may also result inoxidation of the catalyst again requiring the use of a reduction cycleto form the active catalyst species such as a Cr³⁺ composition. Timespent offline reduces overall reactor efficiency.

SUMMARY OF THE INVENTION

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawing.

One aspect of the present invention includes a process ofdehydrogenating an alkane to an alkene, including: (a) feeding an alkanefeedstock and CO to a reactor containing a catalyst comprising Cr₂O₃;and (b) contacting the alkane feedstock with the catalyst to form analkene and H₂; wherein, in the reactor: a portion of the CO fed to thereactor reduces the CrO₃ to form Cr₂O₃ and CO₂.

A second aspect of the present invention includes a process ofdehydrogenating an alkane to an alkene, including: (a) feeding an alkanefeedstock and CO to a reactor containing (i) a catalyst comprising Cr₂O₃and (ii) a heat-releasing material comprising CuO; and (b) contactingthe alkane feedstock with the catalyst to form an alkene and H₂;wherein, in the reactor: a first portion of the CO fed to the reactorreduces the CrO₃ to form Cr₂O₃ and CO₂; and a second portion of the COfed to the reactor reduces the CuO to form Cu and CO₂.

A third aspect of the present invention includes a process ofdehydrogenating an alkane to an alkene, including: (a) feeding an alkanefeedstock and a first amount of CO to a reactor containing a catalystcomprising Cr₂O₃; and (b) contacting the alkane feedstock with thecatalyst to form an alkene and H₂; wherein, in the reactor: a portion ofthe first amount of CO fed to the reactor reduces the CrO₃ to form Cr₂O₃and a portion of the CO₂ reacts with the H₂ to form H₂O and a secondamount of CO; and a portion of the second amount of CO reduces the CrO₃to form Cr₂O₃ and CO₂.

A fourth aspect of the present invention includes a process ofdehydrogenating an alkane to an alkene, including: (a) feeding an alkanefeedstock and a first amount of CO to a reactor containing (i) acatalyst comprising Cr₂O₃ and (ii) a heat-releasing material comprisingCuO; and (b) contacting the alkane feedstock with the catalyst to forman alkene and H₂; wherein, in the reactor: a first portion of the firstamount of CO fed to the reactor reduces the CrO₃ to form Cr₂O₃ and CO₂;a second portion of the first amount of CO fed to the reactor reducesthe CuO to form Cu and CO₂; a portion of the CO₂ reacts with the H₂ toform H₂O and a second amount of CO; a first portion of the second amountof CO reduces the CrO₃ to form Cr₂O₃ and CO₂; and a second portion ofthe second amount of CO reduces the CuO to form Cu and CO₂.

In another aspect of the process of dehydrogenating an alkane to analkene, the alkane feedstock includes a C₂-C₁₀ alkane.

In another aspect of the process of dehydrogenating an alkane to analkene, the alkane feedstock includes a C₃-C₅ alkane.

In another aspect of the process of dehydrogenating an alkane to analkene, the alkane feedstock includes isobutane.

In another aspect of the process of dehydrogenating an alkane to analkene, the catalyst comprising Cr₂O₃ comprise an alumina or zirconiasupport.

A fifth aspect of the invention includes an alkene-containingcomposition obtained by dehydrogenating an alkane in the presence of achromium oxide catalyst.

A sixth aspect of the invention includes a chromium oxide-containingcatalyst obtained by regenerating a catalyst with CO.

BRIEF DESCRIPTION OF THE DRAWING

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawing, wherein:

FIG. 1 shows a graph comparing enthalpy of reaction with CuO versustemperature, for three reducing gases CO, H₂ and CH₄.

FIG. 2 shows a schematic diagram of an alkane dehydrogenation processaccording to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Conventional processes for catalytically dehydrogenating an alkane to analkene use hydrogen-containing gases, such as H₂ and CH₄, in a reductioncycle to reduce the catalyst. Aspects of the present invention insteaduse CO as a reducing gas to reduce the catalyst, during thedehydrogenation reaction. As shown below, and as shown by thermochemicalanalysis, using CO as a reducing gas for the reduction cycle of adehydrogenation process can provide more heat to the reactor bed thanusing H₂. This additional heat can aid in the endothermicdehydrogenation reaction of an alkane to an alkene.

The enthalpy change for the reduction of CrO₃ with H₂ was calculatedbased on standard enthalpies of formation:CrO₃(s)+3/2H ₂(g)→½Cr₂O₃(s)+3/2H ₂O(g)ΔH _(R)°=−336 kJ/mol   (R2)wherein kJ/mol is kiloJoules per mole.

The enthalpy change for the reduction of CrO₃ with CO similarly wascalculated based on standard enthalpies of formation:CrO₃(s)+3/2CO(g)→½Cr₂O₃(s)+3/2CO₂(g)ΔH _(R)°=−397 kJ/mol   (R3)

Both reduction reactions are highly exothermic. However, based on thecalculations, reducing CrO₃ with CO provides an approximately 18%greater enthalpy change compared to reducing CrO₃ with H₂ based oncrystalline CrO₃.

Because of the greater enthalpy change in reducing CrO₃ with CO comparedto reducing CrO₃ with H₂, CO may be advantageously used to reduce insitu a chromium oxide catalyst used in an endothermic alkanedehydrogenation reaction. The additional heat produced by reducing CrO₃with CO and retaining the heat in a reactor means less energy needs tobe supplied when performing a concurrent alkane dehydrogenation in thereactor. In aspects of the invention, additional heat in an amount of 2to 20%, preferably 4 to 18%, 6 to 16%, 8 to 14% or 10 to 12%, based onthe total enthalpy of the reduction of CrO₃ to Cr₂O₃ with CO, incomparison with the reduction of CrO₃ with H₂, is obtained. The use ofCO as a reducing gas to reduce a CrO₃ catalyst provides other benefitsin addition to the enthalpic benefit described above. When an alkane isdehydrogenated to its corresponding alkene, other undesired alkanes andalkenes, as well as coke, may be produced as decomposition byproducts.For example, the dehydrogenation of isobutane (i-C₄H₁₀) to formisobutene (i-C₄H₈) may also produce decomposition byproducts includingpropane (C₃H₈), propylene (C₃H₆), ethane (C₂H₆), ethylene (C₂H₄), andmethane (CH₄) by the following reactions:i-C₄H₁₀→i-C₄H₈+H₂   (R4)i-C₄H₁₀+H₂→C₃H₈+CH₄   (R5)C₃H₈→C₃H₆+H₂   (R6)2CH₄→C₂H₆+H₂   (R7)C₃H₈→C₂H₄+CH₄   (R8)C₂H₆→C₂H₄+H₂   (R9)

The production of these decomposition byproducts requires the presenceof hydrogen (see, e.g., reaction (R5)). Accordingly, it is advantageousin the present invention to provide an alternate reaction pathway forhydrogen, so that decomposition reactions such as (R5) to (R9), as wellas coke formation, are suppressed or eliminated. In aspects of theinvention, the yield of any of CH₄, C₃H₆, C₃H₈, C₂H₆, or C₂H₄ during thedehydrogenation of isobutane (i-C₄H₁₀) to form isobutene, is less than0.1 volume percent (vol %), preferably less than 0.05 vol %, 0.001 vol%, 0.0005 vol %, 0.0001 vol %, 0.00005 vol % or less than 0.00001 vol %based on the total volume of the isobutane subjected to thedehydrogenation reaction.

As described above, reducing CrO₃ with CO in the present inventionresults in the production of CO₂, as shown in reaction (R3). This CO₂may be used as a scavenger to react with hydrogen produced in theconcurrent alkane dehydrogenation reaction, thereby decreasing theamount of hydrogen available for facilitating decomposition reactionssuch as (R5) to (R9), and decreasing coke formation. The reaction of CO₂with H₂ proceeds via the reverse water-gas shift reaction, as follows:CO₂(g)+H₂(g)→CO(g)+H₂O(g)ΔH_(R)°=+41 kJ/mol   (R10)

Decreasing the amount of hydrogen available in the dehydrogenationreactor in this way provides the additional benefit of shifting theequilibrium of the dehydrogenation reaction (R1) toward the productside, further improving reactor performance Additionally, the COproduced in the reverse water-gas shift reaction can be recycled toreduce the chromium oxide catalyst, according to reaction (R3).

In certain aspects of the present invention, the reactor contains aheat-releasing material comprising CuO, in addition to the catalystcomprising Cr₂O₃. Such a heat-releasing material provides heat to theendothermic dehydrogenation reaction via the highly exothermic reductionreaction of CuO with CO.

According to thermodynamic analysis, the reduction process using CO withCuO at 298K (R11) produces extra heat of approximately 48% compared toH₂ (R12). Thus the pre-heating cost for the dehydrogenation can bereduced. Alternatively, the amount of heat-generating materials can bereduced if the heat capacity in the reactor bed is fixed at a certainreaction temperature. Furthermore, similar to the Cr⁶⁺ reduction process(R3) the product gas is CO₂. Thus it can be used as another source forthe in situ scavenger of hydrogen via the reverse water-gas shift (RWGS)reaction (R10). As shown in reactions (R12) and (R13), the reduction ofCuO with H₂ or CH₄ does not produce CO₂, and the exothermicities ofthese reactions are lower than that of CO (R11).CuO(s)+CO(g)→Cu(s)+CO₂(g)ΔH_(R)(298 K)=−127 kJ/mol   (R11)CuO(s)+H₂(g)→Cu(s)+H₂O(g)ΔH_(R)(298 K)=−86 kJ/mol   (R12)CuO(s)+⅓CH₄(g)→Cu(s)+2/3H₂O(g)+⅓CO(g)ΔH_(R)(298 K)=−17 kJ/mol   (R13)

As shown in FIG. 1, thermodynamic analysis reveals that the heatreleased by reducing CuO with CO is much higher than that released byreducing CuO with either H₂ or CH₄, not only at a temperature of 298K in(R11) to (R13), but also a higher temperature suitable for alkanedehydrogenation.

The inventive alkane dehydrogenation process may be performedcontinuously or in a batch operation. In a batch operation, the processmay begin with a fresh catalyst comprising Cr₂O₃. During thedehydrogenation reaction, the CrO₃ may be contacted with CO to formCr₂O₃. Alternatively, the batch process may begin with partially orfully spent catalyst comprising CrO₃, which is initially contacted withCO to form Cr—₂O₃ prior to performing the alkane dehydrogenationreaction. In an exemplary embodiment more than 90% by mass, preferablymore than 95% or 99% by mass of the chromium in the fresh catalyst is inthe form of Cr₂O₃. Subsequent use in a dehydrogenation process may lowerthe amount of Cr present as Cr₂O₃ in the catalyst to form a spentcatalyst in which from 40% by mass or less, preferably from 50%, 60%,70%, 80% or 90% by mass or less of the chromium is in the form of Cr₂O₃.Concurrent regeneration of the spent catalyst with CO forms a catalystin which more than 90% by mass, preferably more than 95% or 99% by massof the chromium is in the form of Cr₂O₃.

A non-limiting embodiment of a continuous process according to the thirdaspect of the invention is shown in FIG. 2. This process includes areactor 100 containing a catalyst comprising Cr₂O₃. An alkane feedstockis fed to the reactor 100, along with CO. The alkane in the alkanefeedstock is dehydrogenated in the reactor 100 by contacting the alkanefeedstock with the Cr₂O₃ catalyst to form an alkene and H₂ according toreaction (R1) above. The CO fed to the reactor 100 is contacted with theCrO₃ to form Cr₂O₃ and CO₂. Any excess, unreacted CO exits the reactor100, along with CO₂ produced according to reaction (R3) above. The COand CO₂ are separated, and the CO and CO₂ may be recycled to the feedfor the reactor 100.

The CO₂ produced in the reactor 100 and any CO₂ recycled to the reactor100 reacts with some or all of the H₂ in the reactor 100 to form CO andH₂O, via the reverse water-gas shift reaction (R4) above. AdditionalCO₂, that is, CO₂ not produced in the reactor 100 or recycled to thereactor 100, may also be supplied to the reactor 100. The alkene, CO andH₂O produced in the reactor 100 exit the reactor and are separated. TheCO from the reactor 100 may be recycled to the feed for the reactor 100.

Although FIG. 2 depicts a single reactor performing catalyticdehydrogenation concurrently with catalyst regeneration, another aspectof the invention includes multiple reactors operating in parallel. Oneor more reactors may perform the catalytic dehydrogenation while one ormore reactors undergo maintenance.

The amount of CO fed to the reactor containing a catalyst comprisingCrO₃ may vary depending on the amount of the catalyst in the reactor,and the extent of conversion from Cr₂O₃ to CrO₃ in the catalyst.Preferably, CO is fed to the reactor at a space velocity of about 0.014l/s based on the catalyst bed volume, and/or at a gas volumetric flowrate of about 2.5 cubic meters per second (m³/s) based on the mass ofthe catalyst.

The amount of CO₂ produced in the reactor by reducing the CrO₃ with COmay vary depending on the amount of the catalyst in the reactor, and theflow rate of CO into the reactor. Additional CO₂ may be supplied to thereactor, to augment the CO₂ produced by reducing the CrO₃ with CO. Theamount of additional CO2 is preferably from 0.1 to 100 times the amountof CO₂ produced by reducing the CrO₃ with CO, more preferably from 1 to50 times, or 5 to 10 times.

The temperature in the reactor during the alkane dehydrogenation mayvary depending on the flow rates of alkane and CO into the reactor, andthe mass of the catalyst. Preferably, the temperature in the reactor isabout 580° C., and the pressure in the reactor is about 1 atmosphere(atm).

The alkane feedstock fed to the reactor performing the alkanedehydrogenation may be derived from a fossil fuel refining process, andmay be supplied from a liquefied petroleum gas source. The alkanefeedstock is preferably fed to the reactor in a gas or vapor phase. Thealkane contains one or more alkanes, and may contain one or morenon-alkane species, such as alkenes and/or alkynes. The alkane in thefeedstock may be a straight-chain alkane or a branched alkane. It ispreferably a C₂-C₁₀ alkane, more preferably a C₃-C₅ alkane, morepreferably isobutane. The alkene produced in the dehydrogenationreaction is preferably a C₂-C₁₀ alkene, more preferably a C₃-C₅ alkene,more preferably isobutene.

The amount of the alkane fed to the reactor performing the alkanedehydrogenation may vary depending on the amount of the catalyst in thereactor, the amount of CO and CO₂ fed to the reactor with the alkane,and the temperature in the reactor. Preferably, the alkane feedstock isfed to the reactor at a space velocity of 0.12 l/s based on the catalystbed volume, and/or a gas volumetric flow rate of 22.2 m³/s based on themass of the catalyst.

The catalyst comprising Cr₂O₃ used for the alkane dehydrogenationpreferably comprises a support component in addition to the chromiumcomponent. The support component may comprise silica, alumina, boria,magnesia, thoria, titania, zirconia, or mixtures of two or more thereof.The support component preferably comprises alumina, zirconia or both.The support may be a zeolite or modified zeolite. The support componentpreferably has a surface area of 50 to 700 square meters per gram, morepreferably 400 to 600 square meters per gram (m²/g), and preferably hasa pore volume of 0.5 to 4 cubic centimeters per gram (m³/g), morepreferably 2 to 3 cubic centimeters per gram.

The chromium component can be combined with the support component invarious manners, such as, for example, forming a co-precipitated tergelof silica, titanium, and chromium. Alternatively, an aqueous solution ofa water soluble chromium component can be added to a hydrogel of thesupport component. Suitable water soluble chromium components include,but are not limited to, chromium nitrate, chromium acetate, and chromiumtrioxide. Alternatively, a solution of a hydrocarbon soluble chromiumcomponent such as tertiary butyl chromate, a diarene chromium compound,biscyclopentadienyl chromium (II), or chromium acetyl acetonate, can beused to impregnate a zerogel, which results from removal of water from acogel. The chromium component is preferably used in an amount sufficientto give about 10 weight percent chromium, more preferably about 20weight percent chromium, based on the total weight of the chromiumcomponent and the support component.

The catalyst is preferably arranged in a fixed bed configuration in thereactor. The catalyst may be used to perform the alkane dehydrogenationreaction for as long as the catalyst retains cost-efficient catalyticactivity.

The single-pass conversion of the alkane in the dehydrogenation reactoris preferably 35% or greater, more preferably 40% or greater, 45% orgreater, 50% or greater, 55% or greater, 60% or greater, 65% or greater,70% or greater, 75% or greater, 80% or greater, 85% or greater, 90% orgreater, or 95% or greater. Unreacted alkane may be separated from theproduct stream leaving the dehydrogenation reactor, for example by analkane-alkene splitter, and recycled to the feed entering the reactor.The overall conversion of the alkane is preferably 70% or greater, 75%or greater, 80% or greater, 85% or greater, 90% or greater, 95% orgreater, 96% or greater, 97% or greater, 98% or greater, or 99% orgreater. The selectivity of the alkane to the desired alkene (forexample, the selectivity of isobutane to isobutene) is preferably 50% orgreater, more preferably 55% or greater, 60% or greater, 65% or greater,70% or greater, 75% or greater, 80% or greater, 85% or greater, 90% orgreater, 95% or greater, 96% or greater, 97% or greater, 98% or greater,or 99% or greater.

The reactor can contain a heat-releasing material comprising CuO, inaddition to the catalyst comprising Cr₂O₃. Such a heat-releasingmaterial provides heat to the endothermic dehydrogenation reaction viathe highly exothermic reduction reaction of CuO with CO. Theheat-releasing material comprising CuO preferably comprises a supportcomponent in addition to the CuO component. The support component maycomprise silica, alumina, boria, magnesia, thoria, titania, zirconia, ormixtures of two or more thereof. The support material may be a zeolite.The support component preferably comprises alumina, zirconia or both.The support component preferably has a surface area of 50 to 700 squaremeters per gram, more preferably 400 to 600 square meters per gram, andpreferably has a pore volume of 0.5 to 4 cubic centimeters per gram,more preferably 2 to 3 cubic centimeters per gram.

Disclosed herein is a process of catalytically dehydrogenating an alkaneto an alkene, using Cr₂O₃ as a catalyst, where the catalyst is reduced(e.g., concurrently) with the dehydrogenation by using CO as a reducinggas. In reducing the catalyst with CO, CO₂ is produced, which may bereacted with H₂ produced by the dehydrogenation, to form CO and H₂O bythe reverse water-gas shift reaction. A CuO heat-releasing material maybe included with the catalyst in the reactor. The CO reducing gasreduces CuO to form Cu and CO₂, releasing heat. The CO₂ produced byreducing the CuO may also be reacted with H₂ produced by thedehydrogenation, to form CO and H₂O by the reverse water-gas shiftreaction.

Set forth below are some embodiments of the process disclosed herein.

Embodiment 1: A process of dehydrogenating an alkane to an alkene,comprising: feeding an alkane feedstock and a first amount of CO to areactor (e.g., a dehydrogenation reactor) containing a catalystcomprising Cr₂O₃; and contacting the alkane feedstock with the catalystto form an alkene and H₂. During the contacting: a first portion of thefirst amount of CO fed to the reactor reduces the CrO₃ to form Cr₂O₃ andCO₂; a portion of the CO₂ reacts with the H₂ to form H₂O and a secondamount of CO; and a first portion of the second amount of CO reduces theCrO₃ to form Cr₂O₃ and CO₂.

Embodiment 2: A process of dehydrogenating an alkane to an alkene,comprising: feeding an alkane feedstock and a first amount of CO to areactor containing a catalyst comprising Cr₂O₃ and a heat-releasingmaterial comprising CuO; and contacting the alkane feedstock with thecatalyst to form an alkene and H₂. During the contacting: a firstportion of the first amount of CO fed to the reactor reduces the CrO₃ toform Cr₂O₃ and CO₂; a second portion of the first amount of CO fed tothe reactor reduces the CuO to form Cu and CO₂; a portion of the CO₂reacts with the H₂ to form H₂O and a second amount of CO; a firstportion of the second amount of CO reduces the CrO₃ to form Cr₂O₃ andCO₂; and a second portion of the second amount of CO reduces the CuO toform Cu and CO₂.

Embodiment 3: The process of any of Embodiments 1-2, wherein the alkanefeedstock comprises a C₂-C₁₀ alkane.

Embodiment 4: The process of any of Embodiments 1-3, wherein the alkanefeedstock comprises a C₃-C₅ alkane.

Embodiment 5: The process of any of Embodiments 1-4, wherein the alkanefeedstock comprises isobutane.

Embodiment 6: The process of any of Embodiments 1-5, wherein thecatalyst further comprises an alumina or zirconia support.

Embodiment 7: The process of any of Embodiments 1-6, wherein asingle-pass conversion of the alkane in the reactor is 55% or greater;preferably 75% or greater; preferably, 80% or greater, and preferably90% or greater.

Embodiment 8: The process of any of Embodiments 1-7, wherein the alkanefeedstock is fed to the reactor at a space velocity of 0.12 s⁻¹ based onthe catalyst bed volume.

Embodiment 9: The process of any of Embodiments 1-8, wherein the processlowers an amount of Cr present as Cr₂O₃ in the catalyst such that 40% bymass or less of the chromium is in the form of Cr₂O₃, preferably 60% orless; preferably 80% or less.

Embodiment 10: The process of any of Embodiments 1-9, further comprisingseparating the CO and the CO₂, and recycling to the reactor at least oneof the separated CO and the separated CO₂ to the reactor.

Embodiment 11: The process of any of Embodiments 1-10, furthercomprising concurrent regeneration the catalyst with CO, wherein theregeneration forms a regenerated catalyst in which more than 90% by massof chromium in the catalyst is in the form of Cr₂O₃; preferably morethan 95% by mass; or preferably more than 99% by mass.

Thus, the foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. As will be understood by thoseskilled in the art, the present invention may be embodied in otherspecific forms without departing from the spirit or essentialcharacteristics thereof. Accordingly, the disclosure of the presentinvention is intended to be illustrative, but not limiting of the scopeof the invention, as well as other claims. The disclosure, including anyreadily discernible variants of the teachings herein, define, in part,the scope of the foregoing claim terminology such that no inventivesubject matter is dedicated to the public.

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/085,234 filed Nov. 26, 2014, which isincorporated herein by reference in its entirety.

The invention claimed is:
 1. A process of dehydrogenating an alkane toan alkene, comprising: feeding an alkane feedstock and a first amount ofCO to a reactor containing a catalyst comprising Cr₂O₃; and contactingthe alkane feedstock with the catalyst to form an alkene and H₂;wherein, during the contacting: a first portion of the first amount ofCO fed to the reactor reduces the CrO₃ to form Cr₂O₃ and CO₂; a portionof the CO₂ reacts with the H₂ to form H₂O and a second amount of CO; anda first portion of the second amount of CO reduces the CrO₃ to formCr₂O₃ and CO₂.
 2. The process of claim 1, wherein the reactor furthercontains a heat-releasing material comprising CuO; and further wherein,during the contacting: a second portion of the first amount of CO fed tothe reactor reduces the CuO to form Cu and CO₂; and a second portion ofthe second amount of CO reduces the CuO to form Cu and CO₂.
 3. Theprocess of claim 1, wherein the alkane feedstock comprises a C₂-C₁₀alkane.
 4. The process of claim 1, wherein the alkane feedstockcomprises a C₃-C₅ alkane.
 5. The process of claim 1, wherein the alkanefeedstock comprises isobutane.
 6. The process of claim 1, wherein thecatalyst further comprises an alumina or zirconia support.
 7. Theprocess of claim 1, further comprising concurrent regeneration thecatalyst with CO, wherein the regeneration forms a regenerated catalystin which more than 90% by mass of chromium in the catalyst is in theform of Cr₂O₃.
 8. The process of claim 1, further comprising concurrentregeneration the catalyst with CO, wherein the regeneration forms aregenerated catalyst in which more than 95% by mass of chromium in thecatalyst is in the form of Cr₂O₃.
 9. The process of claim 1, furthercomprising concurrent regeneration the catalyst with CO, wherein theregeneration forms a regenerated catalyst in which more than 99% by massof chromium in the catalyst is in the form of Cr₂O₃.
 10. A process ofdehydrogenating an alkane to an alkene, comprising: feeding an alkanefeedstock and a first amount of CO to a reactor containing aheat-releasing material comprising CuO and a catalyst comprising Cr₂O₃;contacting the alkane feedstock with the catalyst to form an alkene andH₂; and concurrently regenerating the catalyst with CO, wherein theregeneration forms a regenerated catalyst in which more than 90% by massof chromium in the catalyst is in the form of Cr₂O₃; wherein, during thecontacting: a first portion of the first amount of CO fed to the reactorreduces the CrO₃ to form Cr₂O₃ and CO₂; a second portion of the firstamount of CO fed to the reactor reduces the CuO to form Cu and CO₂; aportion of the CO₂ reacts with the H₂ to form H₂O and a second amount ofCO; a first portion of the second amount of CO reduces the CrO₃ to formCr₂O₃ and CO₂; and a second portion of the second amount of CO reducesthe CuO to form Cu and CO₂.
 11. The process of claim 10, wherein thealkane feedstock comprises a C₂-C ₁₀ alkane.
 12. The process of claim11, wherein the alkane feedstock comprises a C₃-C₅ alkane.
 13. Theprocess of claim 10, wherein the alkane feedstock comprises isobutane.14. The process of claim 10, wherein the catalyst further comprises analumina or zirconia support.
 15. The process of claim 10, furthercomprising concurrent regeneration the catalyst with CO, wherein theregeneration forms a regenerated catalyst in which more than 95% by massof chromium in the catalyst is in the form of Cr₂O₃.
 16. The process ofclaim 10, further comprising concurrent regeneration the catalyst withCO, wherein the regeneration forms a regenerated catalyst in which morethan 99% by mass of chromium in the catalyst is in the form of Cr₂O₃.17. The process of claim 1, further comprising supplying additional CO₂to the reactor in an amount of 0.1 to 100 times the amount of CO₂produced by reducing the CrO₃ with CO.
 18. The process of claim 1,further comprising supplying additional CO₂ to the reactor in an amountof 1 to 50 times the amount of CO₂ produced by reducing the CrO₃ withCO.
 19. The process of claim 1, further comprising supplying additionalCO₂ to the reactor in an amount of 5 to 10 times the amount of CO₂produced by reducing the CrO₃ with CO.